1. Technical Field
The present disclosure relates to micro-light-emitting diodes (micro-LEDs).
2. Description of Related Art
In the recent years, light-emitting diodes (LEDs) have become popular in general and commercial lighting applications. As light sources, LEDs have many advantages including lower energy consumption, longer lifetime, smaller size, and faster switching, and hence conventional lighting, such as incandescent lighting, is gradually replaced by LED lights.
In an LED, when electrons and holes recombine across the semiconductor gap, the recombination energy is emitted in the form of photons and generates light. This recombination mechanism is the so-called radiative recombination. However, when electrons and holes recombine through intermediate electronic states in the semiconductor gap, then the recombination energy is emitted in the form of heat instead of photons, reducing the light emission efficiency of the LED. This recombination mechanism is the so-called non-radiative recombination. On the side surface of an LED, typically there are a large number of surface and defect states. Therefore, a fraction of electrons and holes that are close to the side surface of the LED will non-radiatively recombine through these surface and defect states. This non-radiative recombination generates heat instead of light, considerably reducing the efficiency of the LED. This problem becomes more and more serious as miniaturization of LEDs proceeds to microscale since electrons and holes can spread to the side surface easily in a micro-LED.
Furthermore, since electrons and holes can spread to the side surface easily in a micro-LED, the current density may be too low and uneven within the emitting area of the micro-LED. The low and uneven current density within the emitting area of the micro-LED reduces the efficiency of the micro-LED as well.
Moreover, typically there are a large number of lattice defects in the side surface of an LED due to the etching and/or scribing process. These lattice defects result in leakage currents. As miniaturization of LEDs proceeds to microscale, the ratio of the lattice defects to the lattice sites of a micro-LED increases, thereby raising the ratio of the leakage currents to the total currents of the micro-LED and reducing the efficiency of the micro-LED.
Furthermore, as miniaturization of LEDs proceeds to microscale, the process variation tolerance of micro-LEDs decreases, and therefore the yield rate of micro-LEDs decreases. In addition, transferring, controlling, operating, and handling of micro-LEDs also become more and more difficult.